Power distribution switches are used in power management integrated circuits (PMICs) to distribute power to subsystems. In one example, power distribution switches are used to limit the current flowing to an output device. For example, in a computer system a power distribution switch may couple a power source to an output terminal, thereby supplying power to an attached device. Some devices are currently limited to 0.5 amperes (A) of current for extended periods, but the devices may occasionally draw more current than this limit. If a device overdraws current for too long, the power distribution switch may increase its resistance, thereby reducing the current draw and preventing the device from significantly affecting the voltage level of the power source.
Conventional power distribution switches include analog feedback loops to monitor the input to the power distribution switch for excessive current draw by a device drawing power from the output. In an example, a sense resistor is placed in series with the current supply to generate a sense voltage that is compared to a desired reference voltage at an amplifier. In such arrangements, the output of the amplifier controls the power distribution switch coupling the power source to the output terminal, and increases the resistance of the switch if the sense voltage indicates that too much current is being drawn. However, in the case of a hard short circuit condition (e.g., a condition in which the resistance between an output terminal of the power supply and ground drops to roughly 0.1 ohms (Ω)), large currents may flow through the power distribution switch before the feedback loop can respond to increase resistance of the power distribution switch. This condition may be damaging to the power distribution switch, the power switch device, or may lead to a situation in which the power source voltage is pulled below tolerable levels.